Steel is one of the most commonly used mechanical parts materials. With the constant emergence of new materials for cutting tools, the processing methods for steel materials are becoming increasingly diverse. The most widely used tool material for machining is the carbide series. However, due to the limitations of its own performance, carbide cutting tools are not suitable for the rapid development of high-speed, high-efficiency, and high-precision requirements in the modern machinery industry. Therefore, researches on coated tools, ceramic tools, and super-hard tools have been conducted in recent years. Increasingly. However, these tools are not too costly, that is, they have low strength and toughness, so they are not widely used. The Ti(C,N)-based cermet tool is widely used as a tool material due to its high hardness, good abrasion resistance, and good thermal conductivity. It can also fill between cemented carbide and ceramic tool materials. gap. In addition, through the optimization of the cermet composition, a cutting tool with excellent comprehensive strength, toughness and wear resistance can be prepared, making it suitable for the development of high-speed precision cutting. So far, there are few studies on TiN modified TiC-based cermet tools at home and abroad. This article selects No.45 steel, which is widely used in industrial production, as the target material for cutting. Through specific cutting experiments, it examines and compares the wear performance of new types of cermet tools and traditional cermet tools, Al2O3 tools, and YT15 carbide tools. The practical application of this new type of cermet cutting tool lays a solid foundation.
Table 1 Experimental
composition cermet tool (%) powder TiC TiN (nm) WC Ni Co Mo C mass fraction 48101555161
Fig. 1 SNUN150406 Tool size Chemical composition of the tool The composition of the new cermet cutting tool used is shown in the table to the right. Among them, TiN is a nano powder with a particle size of 30 to 50 nm. The preparation of the cutter is weighed according to the ingredients listed in Table 1. The nano TiN powder is first dispersed by a certain dispersion process, and then a cermet tool is prepared according to a conventional powder metallurgy process. The sintered blank was ground on a M612 face grinder with a 200-mesh diamond wheel to a tool size as shown in FIG. 2 (blade type: SNUN150406). The surface of the tool was observed and polished on a 1 μm diamond polishing paste and etched with a mixed acid of m(HF):n(HCl)=1:1. The microstructure was observed on a HITACHI X-650 scanning electron microscope. The experimental conditions for cutting experiments are as follows: CA6140 lathe; new metallic ceramic tool for cutting tools, traditional Ti(C,N)-based cermet cutting tools (10TiN-16Mo2C-54TiC-20Ni), Al2O3 cutting tools, and YT15 carbide cutting tools; work piece Ø210mm × Steel rod of size 60 mm, normalizing, hardness 21 HRC; cutting conditions for dry cutting; tool mounting angle: a0=9°, g0=-8°, Kr=45°, Kr'= 45°. First, the workpiece to be processed is fixed on the lathe, and the cutter is fixed on the cutter bar and fixed, and cutting is performed according to the set cutting amount. The cutting is suspended at regular intervals, the blade is removed, and the average amount of wear on the back face of the tool is measured under a 40-times tool microscope. The tool is then re-clamped and the cutting continues. The blunt standard flank wear is VB=0.3mm. The HITACHI-650 scanning electron microscope was used to observe the wear patterns of the tool after cutting.
Fig. 2 Organization of cermet tool (SEMx 3000)
2 Results and discussion of the microstructure of the new cermet cutting tool The microstructure of the new cermet cutting tool is shown in Fig. 2. As can be seen from the figure, the structure of the cermet consists of 2 phases (ceramic phase + metal phase). The coarser ceramic phase has a core/shell structure, that is, the core component is a Ti(C,N) solid solution, and the shell component is a (Ti,Mo,W)(C,N) solid solution. The metal phase is an alloy body composed of Ni, Co, and Mo. Compared with the traditional cermet structure, the new cermet structure is finer; this is mainly due to the fact that the addition of nano-TiN reduces the sintering temperature of the cermet and its pinning of the matrix TiC and inhibits the growth of the matrix grain. Tool Wear Pattern and Wear Curve The metal cutting process is a process in which the metal layer on the workpiece undergoes extrusion under the action of a cutter to cause slip deformation, causing fracture, and forming chips. Under normal conditions, the basic form of tool wear is represented by four types of cutting edge wear, rake face wear, flank wear and tip wear, as shown in Figure 3(a). The wear of the flank will appear almost under various cutting conditions, and the measurement is more convenient. Therefore, in this experiment, the flank wear value VB of the tool was used as a reference for judging the bluntness of the tool. A typical wear curve is shown in Figure 3(b). The wear curve of the cermet cutting tool is shown in Fig. 4. When the cutting amount is Vc=300m/min, f=0.1mm/r, ap=1mm, the average wear amount VB(mm) of the flank face of the new cermet cutting tool varies with cutting time t ( The change curve of min). It can be seen from Figure 4 that under this cutting amount, the wear curve of the cermet cutting tool is a typical wear curve and can be divided into three stages. I. Initial wear stage: This stage wears faster because of the presence of micro-roughness, oxide layer, and damage layer on the surface of the newly sharpened cutter, and because of the small contact area between the tool flank and the machined surface during the initial cutting. Concentrated and quickly grinded a narrow surface on the flank. II. Normal wear stage: When a narrow surface is ground in the initial stage, the pressure is reduced, and the wear rate is also stabilized, ie it enters the normal wear stage. This stage is the effective working period of the tool. III. Severe wear stage: When the wear amount is large to a certain extent, the roughness of the machined surface increases, the cutting force and the cutting temperature increase sharply, and the slope of the wear curve sharply increases, so that the tool wear value is large. In order to ensure the quality of processing, this phase should be avoided.
(a) Tool Wear Pattern
(b) Typical Wear Curves Figure 3 Basic Tool Wear Patterns and Typical Wear Curves
(Vc=300m/min, f=0.1mm/r, ap=1mm)
Fig. 4 Normal wear curves of new cermet tools
1. YT15 tool 2. Al2O3 tool 3. Traditional cermet tool 4. New cermet tool Figure 5 Wear curves of new cermet tool and comparison tool
Figure 6 Wear patterns of cermet cutting tools (SEMx 1010)
Comparison of Wear Performance of Cermet Tool and Cemented Carbide Tool YT15 tool, Al2O3 tool, traditional cermet tool and new cermet tool under cutting conditions of Vc=200m/min, f=0.1mm/r, ap=1mm The comparative cutting wear curve is shown in Figure 5. As can be seen from Fig. 5, after the YT15 carbide cutting tool was cut at this cutting amount for 60 min, the average wear amount VB of the back face had exceeded 0.3 mm; for the Al2O3 cutting tool, the cutting time was at VB=0.30 mm. For 76min; for traditional cermet tools, the cutting time can reach more than 200min at VB=0.30mm; however, the VB of the new cermet cutting tool is only 0.23mm at 430 minutes cutting, and the tool is still in the normal wear stage. With this cutting amount, the life of the new cermet cutting tool is much longer than that of the YT15 tool, the Al2O3 tool, and the traditional cermet tool, and the life expectancy thereof is estimated to be more than 500 minutes. Compared with traditional Ti(C,N)-based cermet cutting tools, the new cermet cutting tools have higher tool life because the addition of nano-TiN to TiC-based cermets has a greater effect on the refining of TiC than micro-TiNs. More significant, this can be proved by the literature and Figure 2. The refinement of the cermet structure can effectively improve the comprehensive mechanical properties of the material, and can be used as a tool material to exert its superiority. For the Al2O3 ceramic tool, although it has the advantages of high temperature hardness, good chemical stability, etc., the main disadvantage of the tool material is low bending strength, about 0.4 ~ 0.5GPa. In addition, the thermal conductivity of Al2O3 is about 12.557 W/m·°C, which is 1/2 to 1/5 of cemented carbide, and the coefficient of linear expansion (about 8.0×10-6/°C) is 10% larger than that of cemented carbide. 30%, and low elastic modulus. Therefore, Al2O3 ceramic tool materials are extremely sensitive to mechanical impact. When cutting carbon steel, this type of tool often fails in the form of chipping. Compared with cemented carbide, the reason why cermet cutting tools have a higher tool life is due to the following reasons: (1) The high temperature hardness of the two types of tool materials varies greatly. The YT15 carbide tool is a tungsten-titanium-cobalt (WC-TiC-Co) cemented carbide with a hard phase consisting of WC and TiC and Co as the binder phase. Since the hardness of TiC (HV3200) is higher than that of WC (HV2400), the higher the TiC content, the higher the hardness. Compared with cemented carbide, although the strength and toughness of cermets are lower, their strength decreases slowly with increasing temperature, which makes up for the disadvantages of low strength and can be well applied to plasticity and hardness. Cutting of high materials. (2) The cermet knife has a high antioxidant capacity. The TiO2 protective film formed by TiC oxidation during cutting is very dense and has a lubricating effect, so the wear resistance is high. For carbide cutting tools, WC will be oxidized to form porous WO3 during cutting, and when the tip temperature is above 800°C, WC will react with the steel to form a fragile composite carbide (WFe) 6C. Detrimental to tool wear resistance. Compared with WC, TiC is relatively stable. (3) The cermet knife has a high resistance to crater wear. The temperature at which crater wear starts is generally 850 to 900°C for cemented carbide and 1100 to 1200°C for cermet. (4) The cermet tool has good chemical stability, little affinity with the steel chemistry, and a small coefficient of friction with the workpiece. Therefore, when the cermet cutting tool is used to cut, the adhesion between the tool and the steel can be prevented and the built-up edge cannot be easily generated. The machining accuracy of the workpiece can be significantly improved. The bonding temperature (1120°C) of TiC to workpiece steel 45 is higher than that of WC (1000°C). Therefore, compared with cemented carbide, cermet cutting tools have higher resistance to adhesive wear. The wear profile of the cermet cutting tool Figure 6 shows the wear appearance of the new cermet cutting tool at the cutting rate of Vc=200m/min, ap=0.5mm, f=0.1mm/r. As can be seen from the figure, the wear surface has obvious traces of crack propagation in addition to obvious wear marks and peel pits. The main mechanism of the wear of the cermet tool is abrasive wear, high temperature adhesive wear and diffusion wear. 3 Conclusions Compared with traditional cermets, the new cermet has a much finer structure. Compared with traditional cermet tools, Al2O3 tools and YT15 carbide tools, the new cermet tools have higher tool life and cutting efficiency, and they mainly fail in the form of “wearâ€.
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